This invention relates generally to catalyst exhaust systems for internal combustion engines, and more particularly, to a water-cooled catalyst exhaust system for marine propulsion systems.
Exhaust gases from internal combustion engines are typically treated by a catalyst to purify exhaust emissions by chemical reaction as the exhaust gases flow through the catalyst. The catalyst is placed in the exhaust gas flow path from combustion chambers of the engine to ensure treatment of exhaust gases.
The use of a catalyst, however, presents certain problems. For example, not only are exhaust gases typically hot but the catalyst operates at elevated temperatures to achieve desired chemical reactions, thereby producing thermal stresses that tend to shorten a life span of a catalyst housing surrounding the catalyst. In some application, such as in marine engines, a water jacket may be used to cool the catalyst housing, but if water contacts the catalyst, it can damage the catalyst and render it ineffective. Further, because exhaust gases in marine engines are typically mixed with water and discharged into a body of water below the water line through a rearwardly faced opening formed in a hub of a propeller, rapid deceleration or reverse operation of the propeller tends to drive water backward through the exhaust system and cause the catalyst to be splashed, thereby impairing the catalyst.
In an exemplary embodiment, a catalyst exhaust system for a marine engine includes a catalyst housing having an inlet end, an outlet end, and a passage therethough. The outlet end includes a valve seat, and a water jacket surrounds the catalyst housing. A valve housing is in flow communication with the outlet end and in flow communication with said water jacket to accommodate a valve configured to allow passage of exhaust gases through the catalyst housing during normal operation, but to sealingly engage the valve seat and prevent water from entering the catalyst housing passage and reaching a catalyst therein when engine exhaust pressure drops below a threshold level.
The catalyst housing passage is located in flow communication with combustion chambers of an internal combustion engine, such as a marine engine, and exhaust gases from the combustion chambers are directed through the catalyst to purify the exhaust gases. The valve is biased to a normally closed position, but when exhaust gas pressure in the catalyst housing is sufficiently high, the valve opens and gases flow through the valve for exhaust to the atmosphere through a body of water. The catalyst housing is configured with coolant water passages to deliver coolant water from the engine coolant system to the water jacket surrounding the catalyst housing passage. The water jacket is also in flow communication with the valve housing so that the valve is water cooled as water is mixed with exhaust gases downstream of the catalyst.
In one embodiment, the catalyst housing includes an upper portion, a lower portion, and a gasket therebetween to prevent water from migrating through the joints of the housing and reaching the catalyst. In a further embodiment, the catalyst cooling water jacket includes an exhaust baffle to pressurize water flow into the exhaust stream.
The water jacket cools the catalyst housing and lowers thermal stresses to extend life of the catalyst housing, and the valve protects the catalyst from water contact even during sudden deceleration conditions or reverse operation of the propeller that tends to drive water backward through the exhaust system of an marine engine. The valve is also water cooled, thereby reducing thermal stresses to the valve and extending a working life of the valve. A reliable catalyst exhaust system is therefore provided that is especially advantageous for use in marine engines.